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<TITLE>Filtering Mail with Sendmail</TITLE>
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<H1>Filtering Mail with Sendmail</H1>

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<P><B>Disclaimer</B>:
This preliminary API description is provided for review only.  This
specification may change based on feedback from reviewers, and does
not bind Sendmail to offer this functionality in any release.
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<H2>Introduction</H2>

<P>
Sendmail's Content Management API (milter) provides third-party
programs to access mail messages as they are being processed by the
Mail Transfer Agent (MTA), allowing them to examine and modify message
content and meta-information.  Filtering policies implemented by
Milter-conformant filters may then be centrally configured and
composed in an end-user's MTA configuration file.

<P>
Possible uses for filters include spam rejection, virus
filtering, and content control.  In general, Milter seeks to address
site-wide filtering concerns in a scalable way.  Individual users' mail
filtering needs (e.g. sorting messages by subject) are left to
client-level programs such as <A href="http://www.procmail.org">Procmail</A>.

<P>
This document is a technical introduction intended for those
interested in developing Milter filters.  It includes:
<UL>
<LI>A description of Milter's design goals.

<LI>An explanation of Milter application architecture, including
interactions between the support library and user code, and between
filters and the MTA.

<LI>A specification of the C application programming interface.
<LI>An example of a simple Milter filter.
</UL>

<H2>Contents</H2>

<UL>
<LI><A href="design.html">Architecture</A>
<UL>
    <LI>Design Goals
    <LI>Implementing Filtering Policies
    <LI>MTA - Filter communication
</UL>
<LI><A href="overview.html">Technical Overview</A>
<UL>
    <LI>Initialization
    <LI>Control flow
    <LI>Multithreading
    <LI>Resource Management
    <LI>Signal Handling
</UL>
<LI><A href="api.html">API Documentation</A>
<UL>
    <LI>Library Control Functions
    <LI>Data Access Functions
    <LI>Message Modification Functions
    <LI>Callbacks
</UL>
<LI><A href="installation.html">Installation and Configuration</A>
<UL>
    <LI>Compiling and Installing Your Filter
    <LI>Configuring Sendmail
</UL>
<LI><A href="sample.html">A Sample Filter</A>
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Copyright (c) 2000, 2001, 2003 Proofpoint, Inc. and its suppliers.
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By using this file, you agree to the terms and conditions set
forth in the LICENSE.
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